Catheters are frequently inserted into the human body by means of an aid called a "cannula." A cannula is a flexible tube which serves as a passageway into a blood vessel for a probe or catheter. When a probe or catheter is to remain in the body for an extended period, it is desirable to remove the cannula. However, removal of the cannula is not always a simple task. Frequently, a probe or catheter has an enlarged proximal end which makes the removal of the cannula (sleeve) difficult. This problem has been alleviated by a cannula which separates into two parts as described, for example, in U.S. Pat. No. Re. 13,855 issued Mar. 26, 1985 and in U.S. Pat. No. 4,166,469 issued Sept. 4, 1979. Although the apparatus described expedites removal of the cannula, it requires two hands to remove it, requires a tab at the proximal end of each side of the cannula, requires a sleeve within a sleeve, and requires a line of apertures or particular molecular properties, to ensure that the cannula tears along a longitudinal direction.